The present invention relates to a recording disk data playback apparatus having a capability for playback of both analog and digital recorded data from recording disks, and in particular to a recording disk data playback apparatus which is capable of playback of compact digital audio disks (CDs), LDs having audio and video data recorded thereon in frequency-modulated form, and a type of disk which has the latter video and audio data recorded thereon in frequency-modulated form, together with a digitized audio signal superimposed thereon.
Various types of recording disk data playback apparatus, sometimes referred to as disk players, have been developed. Until recently, such players were divided into two basic types. One type is utilized only for playback of video disks on which video and audio data are recorded in the form of analog signals. Such disks are sometimes referred to as LDs, and this abbreviation will be used for these in the following. With such disks, the video and analog signals are utilized to frequency-modulate a high-frequency carrier signal, and the resultant modulated signal is recorded on the disk. The other type of disk player is utilized for playback of digital audio disks, sometimes referred to as compact disks or CDs, and the latter abbreviation will be used hereinafter for such disks. CDs have audio data recorded thereon in the form of a digital signal of PCM (pulse-code modulation) type, i.e. a carrier signal is modulated by an encoded digital signal representing the audio data, and the modulated signal is recorded on the disk. However in recent years, a new type of recording disk (designated in the following as LDD) has been developed, as described in Japanese patent No. 58-45780) whereby an audio signal which has been digitized, e.g. by a method such as PCM, is converted into a pulse train of form suitable for disk recording, e.g. by applying the EFM (eight-to-fourteen) technique, and this pulse train signal is then superimposed upon a signal which has been produced by FM modulation of a high-frequency carrier by a video signal and an audio signal. The signal which results from this superimposition of the pulse train signal upon the modulated carrier is recorded on the disk. With the latter method, the audio signal is generally separated into two channels, e.g. corresponding to the stereophonic right and left channels, with 2.3 MHz and 2.8 MHz audio carriers being respectively frequency modulated by the two audio channel signals. The frequency spectrum of the recorded signal is such that the the sync tip portions of the video signal correspond to a frequency of 7.6 MHz, the pedestal level to 8.1 MHz, and the white peak level to 9.3 MHz. If the EFM technique is used to record the audio digital signal, then the frequency spectrum of the pulse train will extend from 3T to 11T, where T is the bit period of the PCM signal, 3T corresponds to a pulse frequency of approximately 720 KHz, and 11T is the maximum pulse width and corresponds to a frequency of approximately 200 KHz. This pulse train signal is superimposed on the main video carrier at a level which is approximately 1/10 off the carrier level, or less. Amplification and slicing close to the zero-crossing points are then performed to produce a pulse-width modulated signal, which is used as the recording signal.
With video and audio signals recorded on a disk by the method described above, the frequency spectrum of the RF signal which is produced from the disk will be as shown in FIG. 1. Here, A denotes the digitized audio signal component, B denotes the audio FM signal component, C denotes the color information component of the video FM signal component, and D denotes the brightness component of the video FM signal component.
A very wide dynamic range, e.g. 90 dB or higher is provided by a digitized audio signal with such a system. Thus, a substantial improvement in acoustic fidelity can be attained, by comparison with recording and playback of audio signals using frequency modulation.
In the case of a demodulator of the type generally utilized for demodulation of a digital signal, in a CD playback apparatus, the frequency of the read-out clock signal is held fixed. However with this embodiment of the present invention, data from the demodulator (i.e. the "eight-to-fourteen" EFM demodulator) is temporarily written into a memory, by a write-in clock signal which is synchronized in phase with the playback clock signal, which in turn is synchronized in phase with the rotation of the recording disk, and the stored data are read out from the memory through the use of a read-out clock signal. As a result, time axis deviation components (i.e. jitter) are eliminated.
During playback of an LDD, when a digital signal derived from the playback signal (produced by the video playback apparatus) is demodulated, the playback will already be synchronized in phase with a reference frequency signal which is utilized for video synchronization. In the case of a demodulator utilized in a prior art type of CD player apparatus, a separate reference frequency signal is used to read out data (which was previously output from the PCM demodulator) from the memory. That is, two reference frequency signals are necessary, and if a slight phase deviation should arise between these two reference frequency signals, a time axis deviation will occur between the playback video signal and the demodulated playback audio signal.
Since the speed of rotation of a disk having video data recorded thereon (i.e. a LD or LDD) is different from that of a digital audio disk (CD), it is necessary to provide two different motors to drive the two respective types of disk. With a conventional type of CD disk player, the speed of rotation of the CD drive motor is controlled by a spindle servo system based on a fixed-frequency signal, which is derived from the fixed-frequency read-out clock signal described above. With a prior art type of video disk player, however, the spindle servo system which controls the speed of disk rotation operates based on the horizontal sync signal, extracted from the playback FM video signal. A recording disk data playback apparatus compatible with LDs, LDDs and CDs must therefore include two separate spindle servo systems to control the video disk and digital audio disk drive motors respectively.
For this reason, it is necessary for such a disk player to incorporate means for accurately discriminating between the different types of recording disk which can be played. In particular, it is necessary for the disk player to be provided with means for accurately discriminating between LDs and LDDs, in spite of the fact that these are identical in size. Such discrimination means have not been provided on prior art types of recording disk data playback apparatus.